The Weakest Link in the Bone ‐ Plate ‐ Fracture System; Changes with Time

A retrospective analysis of data from a series of animal studies using the same animal model and methods of evaluation along with one prospective series of animals, provided comparable data on 83 dogs from 0 to 24 weeks post fracture. Closed diaphyseal fractures of the radius were created in 83 adult mongrel dogs. Forty-five were plated with 6 hole DCP stainless steel compression plates and 38 were plated with freeze-dried allograft bone plates. Mechanical evaluation of the strength of the healing bones was carried out at 0, 2, 4, 6, 12, and 24 weeks post fracture and analysis of the mode of failure, the location of failure and correlation with the strength of failure and time post fracture were evaluated for each different type of fixation. Both, the stainless steel and alloplated groups were divided into two subgroups: 1) refracture was carried out after removal of the fixation screws, and 2) refracture was carried out with the plates and screws intact. In the stainless steel plated animals at refracture, if the plates were removed: up to 4 weeks post injury, 100% of the refractures occurred through the fracture site (0% through screw holes); at 8 weeks, 50% (and 50%); at 12 weeks, 0% (and 100%); at 24 weeks, 75% (and 25%). In the stainless steel plated group where the plates were left intact at refracture, most of the refractures occurred at screw holes within the first 8 weeks postfracture, and by 24 weeks, the plates bent but remained attached to the bone, crushing the fracture site. In alloplated bones after screw removal, the refractures occurred at the fracture site consistently over the first 4 weeks; through screw holes at 8 weeks; and with mixed results at 12 and 24 weeks. If the screws were left intact at refracture in the alloplated group, 100% of the refractures occurred through the fracture site at 0 weeks, but from 8 weeks on, refractures were mixed In the stainless steel plated groups, whether the plate was left intact or whether the screws were removed, the refracture strength at screw holes never exceeded 50% of the original strength of the bone.